Method and means for frequency control



SUTER METHOD AND MEANS FOR FREQUENCY Filed June 29, 1942 CONTROL 2 Sheets-Sheet l Dec. 24, 194e. H SUTR 2,413,263

METHOD AND MEANS FOR FREQUENCY CONTROL Filed June 29, 1942 `2 sheets-sheet 2 f --ll- -'rm I I2 I 9 I HIGH FREQ I Q 2| i oscILLAToR I I I |3/C lJ' FIG. 4

ANTENNA MAXIMUM I FREQUENCY wAvE MINIMUM FREQUENCY wAvE SENDING ANTENNA INVENTOR HENRY SUTER Patented Bec. 24, 1946 METHOD AND MEANS FOR FREQUENCY CONTROL Henry Suter, Cincinnati, Ohio, assigner of onefourth to William Ockrant, Cincinnati, Ohio Application June 29, 1942, Serial No. 448,934

6 Claims.

This is a continuation in part of my copending patent application, Serial No. 402,257, led July 12,1941.

This invention relates to a filter or frequency discriminating method or means such as may be used, by way of example, in the technique of' determining the relative velocity of two bodies by the use of electromagnetic waves, preferably of ultra high frequency.

Still a further object of the invention is to provide electrical means for automatically and continuously discriminating against all components of an incoming wave except the maximum or minimum components thereof.

Another object of the invention is to provide a novel electrical filter circuit wherein the characteristics of the filter will be varied in accordance with the amplitude and frequency of the incoming beat frequency.

These and other objects are attained by the means described herein and disclosed in the accompanying drawings, in which:

Fig. 1 is a schematic wiring diagram of an electric circuit of the present invention designed to discriminate against all components of' an incoming wave except the maximum components thereof.

Fig. 2 is a typical magnetization-incremental permeability curve for magnetic materials.

Fig. 3 is a typical attenuation and frequency distribution graph upon which has been superimposed the various frequency components of a typical incoming beat frequency wave.

Fig. 4 is a side schematic diagram illustrating one typical application of the present device as used for determining the speed of objects moving over the surface of the earths surface, such as an automobile or the like.

Fig. 5 is a top schematic view of Fig. 4 wherein one type of operating zone is illustrated with respect to the boundaries of a highway.

Fig. 6 is a schematic diagram illustrating the use of the present device for determining the ground speed of an aircraft.

Fig. 'l is a schematic wiring diagram of an electric filter known as a T lter of the type known to the art as an M derived high pass lter embodying the present invention.

Fig. 8 is a schematic wiring diagram embodying the present invention wherein the filter input is utilized for deriving direct current for controlling the characteristics of filter 44.

In practicing the present invention, a radio transmitter is utilized to propagate and dissemiinate electromagnetic waves, and a radio receiver tuned approximately to the transmitted frequency is utilized to receive the transmitted waves after being reflected.

In the preferred embodiment of the invention both the radio transmitter and receiver are 1ocated on one or the other of the two bodies whose relative rates of travel are being measured.

The transmitted electromagnetic waves are reflected from various objects which may be xed and/or moving relative to the transmitter and receiver. The frequency of the waves reaching the receiver after reflection from the body whose relative motion is to be determined, differs somewhat from the frequency of the transmitted frequency, by reason of the well known Dopplerant beat frequency is an indication of the relative velocity of the two bodies.

With particular reference now to Figs. 4 and 5, it will be observed that when used to indicate the speed of vehicular traffic on a roadway, the radio transmitter and receiver may be contained within a suitable housing denoted generally by the numeral Il). The radio transmitter may comprise any suitable high frequency oscillator II, including an antenna I2, and the receiver may comprise any suitable high frequency receiver I3 such as is illustrated in Radio Handbook, eighth edition, copyright 1941, Editors and Engineers Limited, pages 395 to 398, including an antenna Ill. Preferably, though not necessarily, an electrical shield, denoted generally by the numeral I5, may be interposed between the transmitting and receiving antennae, as illustrated.

Experiment has indicated that when housing It is suspended over a roadway, the opposed parallel side edges of which are indicated by the numerals I6 and I'I respectively, the path of the transmitted radio frequency electromagnetic waves will, under certain conditions, assume the paths indicated bythe closed loops A and B. The radiated waves are reflected from various objects, located within the confines of loops A and B, whether such objects be stationary or moving, and a portion of the reflected electromagnetic waves will be received over the receiving antennaJ I4. In those instances when all of the received waves are reilected from stationary objects, the strength of the resultant wave entering receiver I3, will depend upon and be a ceiver antenna le be comparatively short in relation to the lineal distance of the waves indicated bythe letters C and D, wherein wave C is reflected from wall i8 of a stationary object, such as building I9, and wherein wave D is reflected from a moving object, such as an automobile 20.

It is a well known fact that in order to shorten the path of wave D by one wave-length, the linear distance from vehicle 2E to antennae 'l2 and lil must be decreased by one-half wavelength. By way of example, if it be assumed that oscillator El be generating a frequency of S megacycles per second, or a wavelength of one meter, and if it be further assumed that vehicle 2.53 be approaching antenna i4 at the rate of one meter per second, then wave D, as measured at the receiving antenna lf3, would be 300,000,002 cycles per second. When this waveis beaten against the transmitted wave of 300,000,000 cycles per second, it will produce a beat frequency or note of 2 cycles per second. In other words, the beat frequency or note will be equal to twice the velocity of the vehicle divided by the wave length, assuming, of course, that the direction of vehicular travel is parallel with the longitudinal axis of loops A and B of Fig. 5. By locating the transmitting and receiving equipment close to the roadway, such as alongside of the roadway7 or suspended over the roadway, as illustrated in Fig. 5, a true speed indication of the rate of travel ofvehicles moving toward or away from the device will be given, except forthat period of time When the vehicle is passing the antennae.

AThe beat note produced -by a vehicle, or other object, moving through loops A. and B, may be used to operate directly any suitable speed indieating device, denoted generally in Fig. 4 by the numeral 2|, or the beat note may be first passed through one or more electrical filters. The prime function of such filters would be to select or separate certain beat notes from a variety of frequencies which might be received simultaneously over antenna la as the result of the movement of more than one object at different speeds through the electromagnetic eld. To this end I have provided an electrical liilter circuit which is adapted to automatically and continuously discriminate against all those components of an incoming beat note or wave except the maximum component thereof.

With particular reference now to Fig. l, it will be observed that the output from radio receiver I3 may be connected t0 the'primary 4Q of transformer Alll by means of conductors l2 and 43. Assuming that it is desired to indicate the speed of the fastest moving object through the electromagnetic eld of .the device of Fig. 4, it follows that only the maximum frequency of the numerous frequencies comprisingthe input current to transformer il is to be measured on the frequency or speed indicator ,2 l. To this end, a high pass filter, denoted generally by the numeral 5.4 may be electrically coupled vbetween the secondary 45 of transformer ill and the input side of a suitable amplifier lili, by means of conductors (il, lill, 4S andr 5l?. The attenuation characteristics of filter le aregraphically illustrated in Fig. 3. If it now be assumed that with no input, the characteristic of filter lill is indicated by the dotted curve E, of

Fig. 3, it will be observed that if a complex Wave having frequency components graphically illustrated as ordinates F, G and I-I is introduced, the frequency component F of the incoming wave would be discarded and waves G and I-I amplified. rfhe relatively high output voltage from the ampliiier may be connected, directly to the frequency indicator 2 l rby means of conductors 5I and 52.

In order to eliminate wave G, thereby permitting only the highest wave I-I to pass through to the frequency indicator 2|, the amplifier output may be connected to the input side of a rectifier, 'denoted generally by the numeral 53, by means of conductors 55. and 55. The output of rectifier 53 may be connected to a filter 56 by means` of conductors 5l and 58, in order to eliminate substantialy all 'the AC component in the rectied current. The direct current leaving rectifier 53 is proportional to 'the voltage at the amplifier output, and this current is connected to winding 59 on th@ magnetic core of inductance 60 of filter 44, by means of conductors El and G2, as shown. The amount of direct current flowing through the windings of coil 50, determines the direct magnetizing force in the core of `inductance 60.

It is a well known fact that the incremental permeability shown by a magnetic material to alternatic current superimposed upon a direct current varies with the amplitude of the alternating current, with the value of direct current, and with the previous history of the magnetic material. These relations are explained by Frederick E. Terman in his book Radio Engineering, second edition, pages i8 to 20. A typical curve showing the variation of incremental permeability to a small alternating magnetizing force when superimposed upon a direct magnetizing force of variable magnitude is shown in Fig. 2. The arrows indicate the curves traced for increasing and decreasing direct magnetizing forces. The inductance of a coil having a magnetic core varies with the permeability of the Ycore material, wherefore, it follows that the value of the inductance 60 of filter lll can be made to vary with the amplier output voltage. In this manner, a relatively large output voltage from amplifier '46 may be utilized to change the inductance 60 of lter i4 so as to shift the cut-off frequency to a higher value as indicated by curve I of Fig. 3. In this manner, frequency component G has been effectively and completely eliminated, and in some instances, curve H may be somewhat attenuated to a point where the amount of direct current flowing through inductance 60 is reduced.

From the foregoing, it is apparent that the cutoff frequency is determined by and is a denite function of the output of filter 44 as modified by amplifier t6.

By so designing the high pass filter il-l so that the shape of the attenuation curve at the cut-off frequency is very steep, any given change in the amplitude of the wave component being measured will produce only a small change in the amplier output voltage and in the lter cut-off frequency.

It will be observed that at any one frequency a rise in amplitude of the incoming wave will necessarily produce a rise in the amplifier output voltage in order to increase the cut-off frequency. This rise in output'voltage may be reduced to a practical minimum by proper `filter design, however, it cannot be entirely eliminated. Therefore, a speed indicator operating independently of voltage would 'be ideal, but vthe other rtype may be more practicable.

The use of a standard type of frequency meter requiring a constant operating voltage may be made more practicable Vby usinga transformer or other coupling device between the rectifier input and the amplifier output so that for a given amplifier output voltage the rectified inductance controlling current will increase for increasing frequencies. By this means an impressed signal of constant voltage but variable frequency can be made to change the filter characteristics even though the amplifier output voltage remains constant.'

It should be observed that although amplifier 46 vis shown connected in the circuit of Fig. 1, such use is merely suggestive, since in those instances where sufficient energy may be delivered from the output of filter 44 to operate directly the frequency indicator 2|, the amplier may be dispensed with.

It should likewise be observed that while the filter illustrated in Fig. 1 has but one inductance coil, in some instances it may be preferable to employ a network having more than one inductance, any or all of which may be controlled by direct current. In this manner, closer control of the various filter characteristics may be exercised.

With reference to Fig. 2, it will be observed that by introducing a normal magnetomotive force, or ux density, to the lter inductance core 60 the normal permeability of the core may be shifted along the permeability curve, whereby further increases in the uX density will either increase or decrease the permeability of the core. Therefore, it will be observed that an increase in the rectier output may be utilized to either increase or decrease the inductance in the lter 44.

From the foregoing, it is apparent that by utilizing the variable output of filter 44 to produce a variable direct current, and by then using such direct current to control the permeability of the core of inductance 60 of filter 44, I am able to continuously and automatically vary the characteristics of the filter in such a manner that the amount by which the frequency components of the various incoming waves are suppressed is varied, as the voltage of the filter output is increased.

It should be noted that if desired, filter 44 may be changed from a high pass filter to a low pass filter, in which event only the lowest frequencies would be permitted to pass through to the frequency indicator.

From the foregoing, it is apparent that the speed of the fastest moving object through the electromagnetic field of transmitter II of Figs. 4 and 5, will be automatically indicated on speed indicator 2 I, thereby making it possible and commercially practicable to check the speed of moving objects, such as motor vehicles, directly in miles per hour.

In those instances where it is desirable to have the speed indicator indicate only those vehicle speeds which are in excess of the lawful rate of speed, such as by Way of example, thirtyve.

miles per hour, the attenuation characteristics of filter 44 may be designed as to discard the frequency components of all incoming waves except those whose frequency components are equal to a vehicle speed of thirty-five miles per hour or over.

As previously stated, the beat note produced by a vehicle, or other object, moving through loops A and B, may be used to operate directly any suitable speed indicating device, denoted generally in Fig. 4 by numeral 2|. In some applications it may be preferable to omit the electrical 6. filter and employ a vibrating reed type frequency meter. Various frequencies could then be indicated simultaneously. Should harmonics of the true velocity indicating frequencies be generated,

such maximum frequency harmonics would notv be selected by the equipment for recording to the exclusion of the fundamental frequency. The

small amplitude of reed vibrations caused by har-f monies compared to the relatively large ampli` tude vibrations produced by the fundamentals would indicate them to be spurious.

In cases where the receiver I3 would receive reflected waves simultaneously from vehicles approaching and receding from the equipment I0, the maximum beat frequency would be produced by beating the received waves from vehicles hav-l ing the greatest algebraic difference in their speeds. In addition to the actual speeds of thevarious vehicles, the algebraic difference in speeds would also be indicated. The error of such indications lwould be so obvious that they would -be disregarded. For instance, two vehicles passing each other, one going .3'0 miles per hour, and the other 35 miles per hour, Would produce indications of 30, 35 and 65 miles per hour.

The present invention, in so far as its use on aircraft is concerned, is novel in that a known angle of wave propagation and reception is not required, wherefore, the need for expensive, cumbersome, highly directive transmitting and receiving equipment may be dispensed with without sacrificing reliability or accuracy of performance.

When used to indicate the speed of aircraft,

it is preferable to locate the radio transmitter, receiver and speed indicator on the craft, at any convenient location. As illustrated in Fig. 6, an aircraft 'I0 may be provided with a transmitting antenna I2 and a receiving antenna I4, the radio waves emanating from antenna I2 being propagated in all directions, some of which are indicated by the letters J, K and L. It will be observed that the frequencies will be a maximum for those waves which are reflected from objects which are most nearly in line with the direction of flightof the aircraft. One such maximum frequency reflected Wave is indicated by the letter N. By the same token, it will be noted that the frequency of those waves reflected from objects directly behind the aircraft will be a minimum. Such a minimum frequency wave is indicated by the letter M. It will be observed that the received wave P will have a frequency intermediate the maximum frequency wave N and minimum frequency Wave M.

cies will be produced in the receiver, ranging from y zero up to a certain maximum. The maximum frequency is preferably isolated from the lower frequencies by means of the filter circuit disclosed in Fig. l, whereby the frequency or speed indicator 2| will be actuated by the maximum beat frequency being produced at a particular time.

From the foregoing, it will be observed that I have provided methods of and fully automatic, non-mechanical means for indicating the relative rate of travel between different bodies. It will be observed that in those instances where vehicular speeds are being indicated by the use of directive loops A and B, Fig. 4, the speed of the fastest moving vehicle regardless of its direction of travel, will be indicated on indicator 2|, by reason of the operating characteristics of the circuit of Fig. 1. Such a device makes it possible and practicable to accurately patrol the speed of vehicular traino without the necessity ofv using a separate device for each lane and/or direction of traffic.

As has already been indicated, in some cases it may be preferable to employ a filter network having more than one inductance, any or all of which may be controlled by direct current. For example, consider a "I" filter of the type known to the art as a constant K type filter similar to filter 44 in Fig. ll except that the condenser 90 which is in series with inductance Gil is omitted.

The resistance of the load which is to be connected to, this filter should be equal to the square root of the inductance divided by the capacity. In Fig. l, the load is represented by the input of the amplifier 4t. Since this will remain constant as the lter characteristics are varied, it is obvious that the ratio of inductance to capacity should also remain constanty or, as the inductance is varied, the capacity would also be varied. This can be done indirectly by adding inductances |02 and E93, in series with each of condensers 9| and 92, and controllingr the added inductance as shown in Fig. 7. The reactances of these new arms would be capacitive within the frequency range for which the filter is designed, and its numerical value would be that required to maintain a constant value of the desired load resistance.

It may in some cases be desirable to employ the variable filter herein described in a circuit where the controlling direct currentA is derived from the input to the filter. In this case the characteristics of the filter would be independent of the suppression afforded by that lter, but would depend upon the impressed signal. Such an arrangement is illustrated in Fig. 8, wherein the functions of the various circuit elements are the same as those for Fig. l except that instead of utilizing the amplified filter output for deriving the direct current for controlling the filter, the filter input is employed. By this means, the passed band width, its maximum, or its minimum frequencies can be controlled by the voltage and/or frequencies bf the impressed wave.

It should b-e understood that various modications and changes in the structural details of the device may be made, within the scope of the appended claims, without departing from the spirit of the invention.

What is claimed is:

1. The method of continuously and automatically discriminating against substantially all frequencies below a desired maximum impressed upon a high pass filter including an inductive element, which includes the step of converting the filter output to direct current and of then using said current to control the operating characteristics of the lter by varying the permeability of the inductive element.

2. The method of continuously and automatically discriminating against substantially all frequencies above a desired minimum impressed upon a low pass filter including an inductive element, which includes the step of converting the filter output to direct current and of then using said current to control the operating characteristics of the filter by varying the permeability of the inductive element.

3. In an electric circuit, a high pass lter including an input and an .output and an inductive element having a core of variable permeability, a rectifier having an input and an output,

means electrically connecting the input of said rectifier to the output of said filter, and means energized by the output of said rectifier electrically coupled to said permeable core for continuously and automatically controlling the operating characteristics of said filter, said rectier output being controlled by the unsuppressed frequency components from the filter output, whereby the permeability of the core of said inductive element is controlled by and is a function of the output of said rectifier, for controlling the frequency below which the frequency components are suppressed.

4. In an electric circuit, a low pass filter including an input and an output and an inductive element having a core of variable permeability, a rectifier having an input and an output, means electrically connecting the input of said rectifier to the output of said filter, and means energized by the output of said rectifier electrically coupled to said permeable core for continuously and automatically controlling the operating characteristics of said filter, said rectifier output being controlled by the unsuppressed frequency components from the lter output, whereby the permeability of the core of said inductive element is controlled by and is a function of the output of said rectifier for controlling the frequency above which the frequency components are suppressed.

5. In combination with an electrical circuit including means for receiving multi-frequency signals, of a high pass lter including a core of variable permeability having two windings thereon, one of said windings comprising an inductive element of the lter circuit, means for impressing said signals on said filter, means for rectifying the unsuppressed frequencies passing through said filter circuit, and means connecting the output of said rectifying means to the second winding of the core of said filter for automatically and continuously varying the permeability of the core of said inductive element inversely as the lter output is increased, whereby to eliminate substantially all but the maximum frequency of the received signal, regardless of its strength or frequency value.

6. In combination with an electrical circuit means for receiving multi-frequency signals, of a filter adapted to suppress or discriminate against 55 lower frequencies, means for impressing said multi-frequency signals on said filter, said lter including a core of variable permeability having .two windings thereon, one-of said windings comprising an inductive element of the filter, means 60 for amplifying the unsuppressed frequencies passed by said filter, means for rectifying part of the output of said amplifying means, and means connecting said rectifying means to the second winding of said core for continuously and auto-,f matically varying the permeability of the core of said inductive element inversely as the lter output is increased, to increase the frequency, suppressing characteristics of the lter whereby only the highest frequency of the received signal passes through said filter.

HENRY SUI'ER. 

